I'm sorry but your surrounding your TT with speakers, that's never a good thing. Having speakers that close together you might as well be listening to one of them unless your sitting 20 inches away from them, you'll never get any imaging like that. Have you heard of the magic triangle for speaker imaging? Your setting distance should be the same for left and right speakers, and the speakers should be the same distance apart as the setting distance. So if your sitting 8 feet from the left and right speakers, the left and right speakers need to be apart 8 feet.I feel like that is just a band-aid.
Until you move the speakers or the turntable away from each other your going to get feedback. I don't think your getting vibration as much as the cartridge is picking up the sound waves in the air bouncing off walls.
Heres some things that can help..
Raise the TT up as high as the record display above it.
When playing a record, try taking the dust cover completely off. When it's hinged up, it's a satellite dish, when it's down it's a reflecting point and getting bombarded
with sound waves and it echoes inside it.
Since your still moving in, you might not be setup with to much decor around the room yet. Plants real, or dry or fake ones will help a lot. These help my room and break up reflections around the tables off the back wall.
You need to confirm the turntable input is ok and that feedback is the issue.
We already know it's feedback, in fact I though it was feed back starting at post #1.